The effects of a high-fat, high-fructose, and combination diet on learning, weight, and glucose regulation in C57BL/6 mice.

The objective of the study was to determine the effects of a high-fructose diet, a high-fat diet and a combination high-fructose/high-fat diet on weight gain, blood glucose regulation, and cognitive function in C57BL/6 mice. Thirty-eight male mice aged 7 weeks were placed on one of four different diets for 3 months: standard chow and water (n=8), standard diet and access to a fructose solution as the only intake of water (n=8), high-fat diet and water (n=11), and high-fat diet and fructose solution (n=11). Weights were measured 10 times over a 3-month period. Blood glucose regulation was measured using a glucose tolerance test. Cognitive testing consisted of learning an operant bar-pressing task and was performed in the absence of fructose intake. At the end of the experiment, the density of the fructose-specific glucose transporter GLUT5 was measured in the hippocampus, frontal cortex, sensori-motor cortex and cerebellum. The high-fat and the combined high-fat/high-fructose groups gained significantly more weight than the control group. The high-fat group and combined group had significantly higher levels of blood glucose than the control group. The high-fructose group learned the operant task faster than the control group, but the high-fat/high-fructose group was not different from control indicating that the facilitative effect of prior fructose intake was abolished when a high-fat diet was added. Addition of fructose to the diet did not result in an increase of brain GLUT5 density suggesting that the learning improvement were not dependent on plastic upregulation of GLUT5 fructose transporter. The results show that, contrary to high-fat diets, access to fructose in mice did not lead to increased weight and impaired glucose tolerance. The present experiment confirm the deleterious impact of high-fat diets on glucose regulation and weight but suggest that high-fructose diets, contrary to what has been observed in hamsters, do not have the same effect.